let tree = [
    {
      id: '1',
      title: '节点1',
      children: [
        {
          id: '1-1',
          title: '节点1-1',
          children: []
        },
        {
          id: '1-2',
          title: '节点1-2',
          children: []
        }
      ]
    },
    {
      id: '2',
      title: '节点2',
      children: [
        {
          id: '2-1',
          title: '节点2-1',
          children: []
        }
      ]
    }
  
  ]